Siemens SIMATIC S5 Manual page 288

C.6.1 How is data exchanged?
Overview of data Fig. C-9 illustrates how the DP master and the DP slaves exchange data. In
exchange
the station connecting cycle, the DP master ascertains which stations are
available on the bus. If a station has failed, the IM 308-C detects this state in
the station connecting cycle.
In the data cycle, the IM 308-C sends output data to the slaves and receives
input data.
In the diagnostics cycle, the DP slaves that have experienced a change in
their diagnostic message report this change to the IM 308-C.
The DP master then passes the token (send authorization) to the next DP
master (if there is more than one in the system) = token passing.
Figure C-9 Block diagram illustrating exchange of data between DP master and DP
ET 200 Distributed I/O System
EWA 4NEB 780 6000-02a
Reaction times in the ET 200 distributed I/O system
Start
Station connecting cycle
Data cycle
Slave xxx
yes
has diagnostic
report?
no
Token passing
slave
Steady-state operation
Diagnostics cycle
C
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